From a microbiological perspective, the primary function of normal, intact skin is to control microbial populations that live on the skin surface and to prevent underlying tissue from becoming colonized and invaded by potential pathogens. Exposure of subcutaneous tissue (i.e. a wound) provides a moist, warm and nutritious environment that is conducive to microbial colonization and proliferation.
Since wound colonization is mostly polymicrobial, involving numerous microorganisms that are potentially pathogenic, any wound is at some risk of becoming infected. In the event of an infection a wound fails to heal, the patient suffers increased trauma as well as increased treatment costs. General wound management practices become more resource demanding. Wounds are an enormous problem worldwide. Approximately 1% of the world's population suffers a venous leg ulcer (Ruckley, 1997. Angiology, 48: 67-69). Friedberg et al. estimated the annual cost for dealing with venous leg ulcers in 192 patients to be $1.26 million (Friedberg et al., 2002. J. Wound. Ostomny. Continence. Nurs. 29: 186-192). This equals 6.5 billion of direct wound care cost for every 1 million venous leg ulcer patients. Pressure ulcers are a common and expensive wound care problem in acute care, nursing homes and home care populations. For decubitus ulcer, Stausberg et al. (2005) demonstrated 1% incidence rate along with a 5% prevalence rate for hospital patients (Stausberg et al., 2005. Adv. Skin Wound. Care, 18: 140-145). Bennett et al. found that the management of decubitus ulcers costs approximately 3-4 billion dollars annually in the United Kingdom, which is over 4% of the total National Health Service expenditure in the United Kingdom (Bennett et al., 2004. Ageing, 33: 230-235). In the United States, diabetic foot ulcers in 2004 consumed approximately 10 billion dollars in direct cost (approximately 4% of the total personal health spending of the United States) and another $5 billion in indirect cost (disability, nursing homes, etc.). Diabetic foot ulcers caused over 100,000 major diabetic limb amputations. The cost for each amputation when factoring in associated costs was $100,000 in 2005, resulting in $10 billion in direct cost (Heyneman and Lawless-Liday, 2002. Critical Care Nurse, 22: 52-60). Wounds are becoming an increased portion of the cost of the healthcare system.
Thus, concern among health care practitioners regarding the risk of wound infection is justifiable not only in terms of increased trauma to the patient but also in view of its burden on financial resources and the increasing requirement for cost-effective management within the health care system. Most wound infections are caused by Staphylococcus aureus (20%), Staphylococcus epidermidis (14%), Enterococci spp. (12%), Escherichia coli (8%), Pseudomonas aeruginosa (8%), Enterobacter spp. (7%), Proteus spp. (3%), Klebsiella pneumoniae (3%), Streptococci (3%) and Candida albicans (3%) (CDC Report on common bacterial species associated with wound infections, 1996).
In recent years, there have been numerous efforts to use antibiotics and antimicrobials for the treatment of non-healing, clinically infected wounds. These antimicrobial agents are of varying chemical composition and can include peptides (Zaleski et al., 2006, Antimicrob. Agents Chemother., 50: 3856-3860), antiseptics (U.S. Pat. No. 6,700,032), antibiotics (Rothstein, et al., 2006, Antimicrob. Agents Chemother, 50: 3658-3664; Rittenhouse, et al., 2006, Antimicrob. Agents Chemother. 50: 3886-3888), silver ions/compounds (US patent appl. pub. no. 2005/0035327), chitosan (US patent appl. pub. no. 2006/0210613; U.S. Pat. No. 6,998,509), nitrofurazone (Munster, 1984, J. Trauma 24: 524-525), bismuth thiols (Domenico, et al., 2000, Infect. Med. 17: 123-127), and xylitol (WO 2005/058381).
There have been various attempts by others to create wound care devices such as dressings or bandages, gels and ointments comprising antimicrobial agents. For example, U.S. Pat. No. 3,930,000 discloses the use of a silver zinc allantoinate cream for killing bacteria and fungi associated with burn wounds. Another example is silver sulfadiazine (SILVA-DINE®), which has been shown to be effective when tested in vitro against 50 strains of methicillin resistant S. aureus (MRSA). Numerous products are commercially available with different trade names that employ silver as antimicrobial agents such as STERIPURE®, A.M.Y., ACTICOAT™, ACTISORB®, and SILVERLON®.
U.S. Pat. No. 7,091,336 teaches the process of making a gel containing gellan gum that increases in viscosity once applied to the wound to form an immobile gel. One example of a commercially available wound gel is INTRASITE®, contains carboxymethyl cellulose as a main ingredient. U.S. Pat. No. 6,700,032 discloses the application of triclosan in wound dressing fabricated from a natural or synthetic film-forming material, such as hydrophobic polymeric membrane. DeBusk and Alleman disclose a wound dressing that has been infused with a suspension of starch hydrolysate containing collagen and α-tocopherol acetate (U.S. patent appl. Pub. No. 2004/0001878). Wounds, in particular those occurring in the skin as second and third degree burns, stasis ulcers, tropic lesions, such as decubitus ulcers, severe cuts and abrasions that are commonly resistant to the natural healing process, may be treated with the infused dressing. Progress has been made on developing wound care devices, but each of the wound etiologies are increasing at double digit rates annually, causing the number of wounds to double every 4-5 years (Drosou et al., 2003, Wounds, 15:149-166).
Wounds often have multiple barriers to healing. Wound healing and infection is influenced by the relationship between the ability of bacteria to create a stable, prosperous community within a wound environment and the ability of the host to control the bacterial community. Since bacteria are rapidly able to form their own protective microenvironment (biofilm) following their attachment to a surface, the ability of the host to control these organisms is likely to decrease as the biofilm community matures. Within a stable biofilm community, interactions between aerobic and anaerobic bacteria are likely to increase their net pathogenic effect, enhancing their potential to cause infection and delay healing. Over the last few years, some have linked biofilm to chronic wounds (Mertz, 2003, Wounds, 15: 1-9). Microscopic evaluation or chronic wounds showed well organized biofilm with extracellular polymeric substance adhered around colony bacteria in at least 60% of the chronic wounds (Mertz, 2003, Wounds, 15: 1-9).
In addition to a direct effect on wound healing by the production of destructive enzymes and toxins, mixed communities of microorganisms may also indirectly affect healing by promoting a chronic inflammatory state. Prolonged exposure to bacteria within a chronic wound leads to a prolonged inflammatory response, resulting in the release of free radicals and numerous lytic enzymes that could have a detrimental effect on cellular processes involved in wound healing. Proteinases released from a number of bacteria, particularly Pseudomonas aeruginosa, are known to affect growth factors and many other tissue proteins that are necessary for the wound healing process (Steed et al., 1996, J. Am. Coll. Surg, 183: 61-64; Travis et al., 1995, Trends Microbiol. 3: 405-407). The increased production of exudates that often accompanies increased microbial load has been associated with the degradation of growth factors and matrix metalloproteinases (MMPs), which subsequently affect cell proliferation and wound healing (Falanga et al., 1994, J Invest Dermatol. 1: 125-127).
Dental plaque is a host-associated biofilm that adheres to the tooth surface both above and below the gingival margin. Dental plaque consists mainly of microorganisms with a small number of epithelial cells, leukocytes, and macrophages in an intracellular matrix. It has been postulated that there are approximately 300 to 400 different bacterial species in dental plaque (Moore, 1987, J. Periodont. Res. 22: 335-341). Periodontal disease comprises a collection of inflammatory conditions of the periodontium (gingiva, periodontal ligament, cementum, and alveolar bone) due to a chronic bacterial infection, i.e., dental plaque. Over 90% of the population of the United States is affected by periodontal disease (Brown et al., 1996, J. Dent. Res. 75: 672-683).
In addition to periodontal diseases, other conditions/diseases caused by biofilms include cystic fibrosis, pneumonia, native valve endocarditis and otitis media (Costerton et al. Science 1999 284:1318-1322). Biofilm is also implicated in the infection of various medical devices such as urinary catheters, mechanical heart valves, cardiac pacemakers, prosthetic joints, and contact lenses (Donlan, R. M. 2001 Emerging Infect. Dis. 7:277-281). For example, urinary tract infection (UTI) is the most common hospital-acquired infection, accounting for up to 40% of all nosocomial infections. The majority of cases of UTIs are associated with the use of urinary catheters, including trans-urethral folcy, suprapubic, and nephrostomy catheters. These urinary catheters are inserted in a variety of populations, including the elderly, stroke victims, spinal cord-injured patients, post-operative patients and those with obstructive uropathy. Despite adherence to sterile guidelines for the insertion and maintenance of urinary catheters, catheter-associated UTIs continue to pose a major problem. For instance, it is estimated that almost one-quarter of hospitalized spinal cord-injured patients develop symptomatic UTIs during their hospital course. Gram-negative bacilli account for almost 60-70%, Enterococci for about 25%, and Candida species for about 10% of cases of catheter-associated UTI.
Furthermore, indwelling medical devices including vascular catheters are becoming essential in the management of hospitalized patients by providing venous access. The benefit derived from these catheters as well as other types of medical devices such as peritoneal catheters, cardiovascular devices, orthopedic implants, and other prosthetic devices is often offset by infectious complications. The most common organisms causing these infectious complications are Staphylococcus epidermidis and Staphylococcus aureus. In the case of vascular catheters, these two organisms account for almost 70-80% of all infectious organisms, with Staphylococcus epidermidis being the most common organism. Fungi also form biofilms of clinical significance. Candida albicans, a fungal agent, accounts for 10-15% of catheter infections.
Bacteria and fungi growing in biofilms exhibit increased resistance to antimicrobial agents and are nearly impossible to eradicate using known techniques. The present invention teaches applications of an antibiofilm enzyme DispersinB™-based antimicrobial composition in devices, methods for preparing such devices, and methods of treating wounds and oral infections.